The invention relates to a heating device, particularly a vehicle auxiliary heating device having a combustion chamber surrounded by a heat exchanger. Inner fins define exhaust gas channels at an inner surface of the heat exchanger, and the inner side of the heat exchanger surrounds the flow of hot combustion gases exiting from the combustion chamber. At its outer side. the heat exchanger is surrounded by a flow of a liquid heat exchange medium, such as a liquid coolant, water, or the like, that enters by an inlet, and leaves via an outlet, provided in a housing encasing the heat exchanger.
Heating devices operating with a gaseous heat exchange medium, like air, are referred to as so-called air heating devices. Examples of such devices are described in German Offenlegungsschrift No. 35 09 349 or French Pat. No. 1,409,337. In such air heating devices it is known to provide a heat exchanger in which the contour formed by outwardly directed longitudinal fins (i.e., the locus of points formed by the free ends of the fins) is rectangular, quadrangular or of similar shape. In the air heating device of French Pat. 1,409,337, the heat exchanger is of a cuboid configuration, while an inner cavity of the heat exchanger through which the hot combustion gases travel is rectanguloid and contains inwardly directed fins which define exhaust gas channels. However, a closed end of this heat exchanger, at which the flow of exhaust gases is reversed, is curved, i.e., it is cross-sectionally a hemi-spherical configuration.
In contrast thereto, heating devices operated with a liquid heat exchange medium, like a liquid coolant, water, or the like, referred to as so-called water heating devices, are known. Conventionally, water heating devices have been provided with hollow cylindrical heat exchangers for the purpose of obtaining uniform flow penetration and flow circulation of the liquid heat exchange medium through the heat exchanger. U.S. Pat. No. 4,624,218 is an example of a water heating device and has heat exchanger fins extending radially from its inner surface, the free ends of which are disposed along a circle having the center axis of the combustion chamber as its center. A liquid heat transfer medium enters an annular flow-through space between the heat exchanger and an outer housing (formed by integrally joined inner and outer jackets) in proximity to a closed end of the heat exchanger and exits via an outlet near the opposite end thereof. Furthermore, in one embodiment, the housing has a quadrangular exterior shape, although it is internally cylindric. Another example of a water heater is shown in U.S. Pat. No. 4,395,225. The heater shown there has an outwardly projecting helical fin on an outer surface of the heat exchanger, and, again, the liquid heat transfer medium enters in proximity to the closed end of the heat exchanger and exits at the opposite end thereof.